In connection with manufacturing of small structures, such as semiconductors, e.g. integrated circuits or memory media (CD, CD-ROM, DVD, hard disks etc.), imprint lithography may sometimes be used, particularly nanoimprint lithography, which is described in more detail in e.g. WO01/42858A1 and WO01/69317, which are hereby incorporated by reference.
Imprint lithography essentially comprises transferring a relief pattern from a patterned surface, which is referred to as a “stamp”, onto a moldable surface, which is referred to as a “substrate”. The substrate is normally provided with a moldable film. The substrate often consists of a metal- or silicon based material which is provided with e.g. a polymer film.
During the imprint process, the stamp is pressed against the substrate at a pressure which is high enough to cause the pattern on the stamp to form an imprint in the moldable film.
Subsequently, the substrate may be subjected to exposure to e.g. radiation (such as UV-radiation) or etching, whereby parts of the pattern in the moldable film are wholly or partially removed or hardened. This imprint process may be preceded by or followed by application of further layers of moldable film, further imprint steps or any treatment by means of other known semiconductor manufacturing techniques.
In connection with imprint lithography, it may be desirable to heat the moldable film in order to make it softer and thus to facilitate the transfer of the pattern.
Since the structures manufactured using this technique may be very small, in the order of a few nanometers (i.e. millionths of a millimeter), a very small change in the size of a substrate or a template may cause problems in positioning the pattern that is to be transferred. Typical substrates used for imprint lithography may exhibit temperature coefficients in the order of 0.01% per degree F. Thus, heating a substrate having a diameter of e.g. 20 cm from e.g. 25 degrees C. to around 300-400 degrees C. to provide a change of size in the order of 0.2-0.4 percent, i.e. 0.4-0.8 mm. Also, whereas a typical substrate nay be made from aluminum, having a temperature coefficient of 24*10−6/F, the stamp may be made from nickel having a temperature coefficient of 11*10−6/F. This causes difficulties in the operation of lithography equipment, since the heat expansion of the substrate may be twice as large as the heat expansion of the stamp.
One example of a situation where it may be very important that the stamp and the substrate are accurately aligned is where several patterns are to be provided on one substrate, e.g. through a plurality of lithography operations. Another example is the situation with a double-sided substrate, where the patterns provided on the two sides need to be aligned.
Prior art procedures and devices for alignment are provided in e.g. U.S. Pat. No. 5,669,303 and U.S. Pat. No. 5,947,027. According to these documents, the stamp is aligned optically by the use of a pattern that is arranged on the substrate.
The prior art methods and devices for aligning the substrate and the stamp do not take the heat expansion into adequate consideration. There is thus a need for a method and a device that enable accurate alignment and positioning of a stamp and a substrate, even when the size of the substrate changes as a consequence of it being heated.